<!DOCTYPE HTML>
<html>
<head>
  <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
  <title>无标题文档</title>
  <script>

    //hasOwnProperty : 看是不是对象自身下面的属性
    var str = new String();
    console.log(str);
    var arr = [];
    arr.num = 10;
    arr.num2 = 20;
    Array.prototype.num2 = 20;

    console.log(arr.num2);

    //alert(  arr.hasOwnProperty('num')  );  //true

    //alert(  arr.hasOwnProperty('num2')  );  //false


    var duo_wei_array = new Array([1], [2], [3]);
    console.log(duo_wei_array);

  </script>
</head>

<body>
</body>
</html>
